1. Field of the Invention
The present invention relates to radio frequency identification ("RFID") tags, and more particularly, to an RFID tag that can measure time and detect environmental changes.
2. Description of Related Art
In the automatic identification industry, the use of RFID tags has grown in prominence as a way to track data regarding an object to which the RFID tag is affixed. An RFID tag generally includes a semiconductor memory in which digital information may be stored, such as an electrically erasable, programmable read-only memory (EEPROMs) or similar electronic device. Under a technique referred to as "backscatter modulation," the RFID tags transmit stored data by reflecting varying amounts of an electromagnetic field provided by an RFID interrogator by modifying their antenna matching impedances. The RFID tags can therefore operate independent of the frequency of the energizing field, and as a result, the interrogator may operate at multiple frequencies so as to avoid radio frequency (RF) interference, such as utilizing frequency hopping spread spectrum modulation techniques. The RFID tags may either be passive, in which they extract their power from the electromagnetic field provided by the interrogator, or active, in which they include their own power source.
One of the many advantages of RFID tags is that they can be manufactured in very small, light weight and inexpensive units. Passive RFID tags are particularly cost effective since they lack a power source. In view of these advantages, RFID tags can be used in many types of applications in which it is desirable to track information regarding a moving or inaccessible object. One such application is to affix RFID tags to work pieces moving along a conveyor belt of an assembly line. The RFID tags would contain stored information regarding the particular assembly requirements for the work piece to enable automated equipment to operate on the work piece and perform certain tasks unique to the work piece requirements. This way, products having different assembly requirements can be sent down the same assembly line without having to modify the assembly line for each unique requirement. Another application for RFID systems is to collect information from a moving motor vehicle, such as for vehicle toll collection.
A drawback of conventional RFID tags is that they are not able to measure a given length of time, or more specifically, to measure the time that the RFID tag is exposed to a given environmental condition. This ability would be very desirable for RFID tags attached to items that are sensitive to time and environment, such as perishable foods. A time-tracking feature would enable the seller to determine the precise age of the goods they are selling. This would be beneficial to both the seller, who could maximize his profit, and the consumer, who would be given accurate information regarding the food being bought. Moreover, an RFID tag that can detect and report on environment conditions would be further beneficial in the perishable food applications because conditions such as an unacceptably high or low temperature, humidity, or pressure, as well as exposure to certain undesirable gasses could be monitored to determine the food's freshness. Timing and environmental tracking features would also be beneficial for many other applications including the parcel delivery business where certain items to be shipped could be sensitive to time or environment.
It is therefore an object of the present invention to provide an RFID tag with timing capabilities. It is a further object of the present invention to provide an RFID tag with an environment module to detect certain environmental conditions and measure the length of time that an RFID tag is exposed to the environmental conditions.